As is well known, the demand for semiconductor devices has been increasing. Various types of contacts, (e.g., contact holes), have been recently developed for semiconductor devices. The contact hole is usually filled with a conductive metal, (e.g., tungsten), to thereby electrically connect a silicon substrate with a wiring board.
FIG. 1 is a cross-sectional view of a contact of a conventional semiconductor device. A conventional method for forming the contact of the semiconductor device will now be described:
An insulating layer is formed on a substrate 1. The insulating layer is then etched to thereby form a contact hole 2. An active region of the substrate 1 is exposed through the contact hole 2. A tungsten diffusion barrier 3, (e.g., a CVD TiN (chemical vapor deposition titanium nitride) layer), is deposited on the sidewalls and an undersurface of the contact hole 2. Thereafter, the contact hole 2 is filled with tungsten by depositing tungsten on the tungsten diffusion barrier 3 to thereby form a tungsten plug 4. Subsequently, an Al line 5 is deposited on the tungsten plug 4.
The above-mentioned deposition of the CVD TiN layer is usually executed by a MOCVD (metal-organic chemical vapor deposition) method. As a result, many impure atoms, (e.g., C, N, O and the like), are left in the CVD TiN layer. Leakage current can flow through these impure atoms. To reduce the leakage current, attributes of the CVD TiN layer may be enhanced by performing an N2/H2 plasma treatment. That is, the impure atoms in the CVD TiN layer can be reduced by the N2/H2 plasma treatment.
However, because of the anisotropic property of the N2/H2 plasma treatment, the sidewalls of the contact hole 2 cannot be treated with the N2/H2 plasma treatment. Since the attributes of the sidewalls of the contact .hole 2 are not enhanced by the N2/H2 plasma treatment, the leakage current may flow through the sidewalls. Therefore, the yield and the reliability of the manufactured semiconductor devices are degraded.